The present invention generally concerns fluid mixing apparatus, and more particularly in-line mud shearing apparatus for thoroughly mixing and dispersing mud particles in a mud fluid medium in well drilling operations.
Mud is a dense fluid mixture comprised essentially of water, fine soil and clay particles, and dispersion and surfactant additives, and it is used in oil and gas well drilling and workover operations to control the reservoir pressure in a well. The head or pressure of the column of fluid in the well bore must exceed the reservoir pressure at the bottom of the well to prevent the well from flowing or possibly blowing out during drilling or workover operations. The fine soil and clay particles mixed with and held in suspension in the water significantly increase the effective weight or head of the column of fluid in the well bore to control wells bored into higher pressure reservoirs. Consenquently, it is essential that the fine soil or clay particles be thoroughly dispersed and held in suspension in the water medium. Chemical additives are available to aid in this regard, but thorough mixing is required, and the mud is kept constantly circulating by pumping it down the drill pipe or tubing to the bottom of the well bore and back out through the annular space between the drill pipe and the side of the well bore both to maintain a uniform mixture of the mud and to carry drilled cuttings and debris out of the well bore.
It is customary to add the fine soil and clay particles and other additives to the water fluid medium to formulate the mud in a pit or mixing tank for that purpose. Then the mixture is mechanically stirred and agitated in the pit or mixing tank by use of mechanical devices or more sophisticated laser or sonar devices in order to achieve a satisfactory mixture and dispersion of the mud particles in the fluid medium. While such devices and methods are successful to some extent in obtaining a uniform mixture and dispersion of the mud particles in the fluid several problems have heretofore remained unsolved. Such devices are expensive, complex, and somewhat inefficient to operate. For example, mechanical and jet type mixers used in the mixing tank or mud pit often cause air entrainment in the mud fluid which not only results in a mud which has less density than desired but which also could result in formation of larger bubbles of entrapped air at critical locations in the mud flow circuit as well as unnecessary turbulence and cavitation. Further, while it is customary to discharge the mud fluid into the well bore through nozzles in the bit at the bottom of the drill pipe to jet cuttings and debris away from the bit and thereby resulting in some shearing of the fluid, the location of such shearing at the most remote portion of the mud flow circuit under high temperature and pressure bottom hole conditions is neither desirable nor thoroughly effective to significantly enhance the mud mixture and dispersion of particles in the fluid medium.